The supply of a heat engine consists mainly in inserting into a combustion chamber an intake air flow and a liquid fuel vaporized in the intake air flow. The mixture of the air flow and the fuel is achieved in the combustion chamber or upstream of the latter in the intake circuit of the heat engine.
With certain fuels, such as diesel, the starting of the engines is made difficult when the ambient temperature is below approximately 5° C.: the temperature of the air-diesel mixture at the end of compression is not sufficient to cause the mixture to self-ignite. This results in difficulties, if not an impossibility, of starting the heat engine, and an imperfect combustion so long as the engine is not hot enough.
To prevent this disadvantage, it is known practice to heat up the air-diesel mixture by means of a heating system consisting of preheating plugs installed in the cylinder head of the heat engine in order to lead either directly into the combustion chamber or into the turbulence chamber of the heat engine. This heating system is relatively costly because of the necessary installation of plugs on the cylinder head, an installation that also has an influence on the space requirement of the cylinder head.
It is also known practice to heat the intake air by means of a heating grid extending into the intake duct. Because of the pressure losses caused by the grid, this heating device can be used only in heat engines of large cubic capacity.